The CGT in Bulgaria was changed around 2 years ago or so.
Basically as long as you don't sell 2 houses in the same tax year then you are exempt.
It used to be 15% and 0% after 5 years.
But if you pay nothing in Bulgaria you still have to pay the 18% in the UK.
So if i was you i would get onto the tax guys in the Uk government and tell them your predicament.
I dont think you will pay any CGT in Bulgaria, so you only should have to deal with your own Tax people in your country so you should be able to get around it.
Is this right ? i think it is